Rare Coexisting Diseases
A variety of rare disorders may influence the selection and conduct of anesthesia (Table 23-1) (Dierdorf SF, Walton JS. Anesthesia for patients with rare coexisting diseases. In: Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Ortega R, Stock MC, eds. Clinical Anesthesia. Philadelphia: Lippincott Williams & Wilkins; 2013:612–640). Advances in molecular medicine continue to clarify disease mechanisms and provide the basis for new therapies.
I. Musculoskeletal Diseases
Musculoskeletal diseases (muscular dystrophies) are characterized by a progressive loss of skeletal muscle function (cardiac and smooth muscle are also affected).
Duchenne muscular dystrophy is caused by a lack of production of dystrophin, a major component of the skeleton of the muscle membrane characterized by painless degeneration and atrophy of skeletal muscle.
The genetic defect is sex linked (manifests only in males), and symptoms manifest between 2 and 5 years of age (creatine kinase may be increased before symptoms appear). Death is usually secondary to congestive heart failure or pneumonia.
Axial skeletal muscle imbalance produces kyphoscoliosis, which often requires surgical correction.
Involvement of cardiac muscle is reflected by a progressive loss of the R-wave amplitude on the lateral precordial leads of the electrocardiogram (ECG). Routine echocardiography can provide important information about cardiac function. Progressive loss of myocardial tissue results in cardiomyopathy, ventricular dysrhythmias, and mitral regurgitation.
Treatment of cardiac dysfunction includes angiotensin-converting enzyme inhibitors, β-adrenergic blockers, and dysrhythmia surveillance.
Degeneration of respiratory muscles (reflected by spirometry) results in an ineffective cough with retention of secretions and pneumonia.
Management of Anesthesia
Significant complications from anesthesia in patients with muscular dystrophy are secondary to the effects of anesthetic drugs on myocardial and skeletal muscle.
Reports of cardiac arrest associated with rhabdomyolysis and hyperkalemia have occurred with volatile anesthetics alone or in combination with succinylcholine (SCh).
Susceptibility to malignant hyperthermia is unpredictable.
It may be prudent to use intravenous anesthetics and avoid volatile anesthetics and SCh for patients with muscular dystrophy.
Degeneration of gastrointestinal smooth muscle with hypomotility of the intestinal tract and delayed gastric emptying in conjunction with impaired swallowing mechanisms may increase the risk of perioperative aspiration.
Table 23-1 Coexisting Diseases that Influence Anesthesia Management | ||||||||||||||||||||||||||||
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II. The Myotonias
The myotonias are characterized by delayed relaxation of skeletal muscle after voluntary contraction owing to dysfunction of ion channels in the muscle membrane.
Clinical features include diabetes mellitus, thyroid dysfunction, adrenal insufficiency, and cardiac abnormalities (e.g., conduction delays, heart block [sudden death], tachydysrhythmias, cardiomyopathy).
Pulmonary function studies demonstrate a restrictive lung disease pattern, mild arterial hypoxemia, and diminished ventilatory responses to hypoxia and hypercapnia.
Pregnancy may produce an exacerbation of myotonic dystrophy, and congestive heart failure is more likely to occur during pregnancy.
Management of Anesthesia
SCh produces myotonia and should not be administered to these patients. The response of these patients to nondepolarizing muscle relaxants may be enhanced. Reversal with neostigmine may provoke myotonia. The response to the peripheral nerve stimulator must be carefully interpreted because muscle stimulation may produce myotonia (misinterpreted as sustained tetanus when significant neuromuscular block still exists).
Patients with myotonia are very sensitive to the ventilatory depressant effects of opioids, barbiturates, benzodiazepines, and volatile anesthetics.
No specific anesthetic technique has been shown to be superior for patients with myotonic dystrophy. Propofol infusions may be acceptable. Inhaled anesthetics may be used, but close monitoring of cardiac rhythm and cardiovascular function is indicated.
III. Familial Periodic Paralysis
The familial periodic paralyses are a subgroup of diseases referred to as skeletal muscle channelopathies. The common mechanism for these diseases appears to be a persistent sodium inward current depolarization that causes muscle membrane inexcitability and subsequent muscle weakness (Table 23-2).
Hyperkalemic periodic paralysis is characterized by episodes of myotonia and muscle weakness that may last for hours after exposure to a trigger (see Table 23-2).
Hypokalemic periodic paralysis is caused by a defect in the calcium ion channel (see Table 23-2).
Management of Anesthesia
The primary goal of the perioperative management of patients with both forms of periodic paralysis is the maintenance of normal potassium levels and avoidance of events that precipitate muscle weakness (alkalosis owing to hyperventilation, carbohydrate loads, hypothermia).
Short-acting muscle relaxants are preferred, and the response should be monitored with a peripheral nerve stimulator. SCh should be avoided because it may enhance potassium release from skeletal muscle cells.
The ECG should be monitored for evidence of hypokalemia and associated cardiac dysrhythmias. (Serum potassium concentration should be measured during prolonged operations.)
Avoidance of carbohydrate loads, hypothermia, and excessive hyperventilation is prudent.
Table 23-2 Clinical Features of Familial Periodic Paralysis | |
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Table 23-3 Summary of the Different Presentations of Myasthenia Gravis | |||||||||||||||||||||||||||||||||||
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Table 23-4 Osserman Staging System for Myasthenia Gravis | ||||||||||||
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IV. Myasthenia Gravis
Myasthenia gravis is an autoimmune disease with antibodies directed against the nicotinic acetylcholine receptor or other muscle membrane proteins (Table 23-3). The majority of patients have abnormalities of the thymus (thymoma, thymic hyperplasia, thymic atrophy).
The clinical hallmark of myasthenia gravis is skeletal muscle weakness (increased by repetitive muscle use) with periods of exacerbation and remission (Table 23-4).
Neonatal myasthenia begins 12 to 48 hours after birth and reflects transplacental passage of antiacetylcholine antibodies.
Focal myocarditis and atrioventricular heart block may be present.
Treatment includes administration of anticholinesterase drugs, thymectomy, corticosteroids, and immunosuppressants. Whereas underdosage with anticholinesterase drugs results in skeletal muscle weakness, overdosage leads to a “cholinergic crisis.” The role of thymectomy for the treatment of myasthenia is not clearly established.
Management of Anesthesia
The primary concern is the potential interaction among the disease, treatment of the disease, and neuromuscular blocking drugs. Patients with uncontrolled or poorly controlled myasthenia are exquisitely sensitive to even small (defasciculating) doses of nondepolarizing muscle relaxants.
The variability in response to different muscle relaxants warrants careful monitoring with a peripheral nerve stimulator and its correlation with clinical signs of recovery from neuromuscular blockade. Short- or intermediate-acting nondepolarizing muscle relaxants are usually recommended.
Myasthenic Syndrome (Lambert-Eaton Syndrome)
The myasthenic syndrome is a disorder of neuromuscular transmission associated with carcinomas, particularly small cell carcinoma of the lung. (This syndrome should be suspected in patients undergoing diagnostic procedures, such as diagnostic bronchoscopy, mediastinoscopy, or exploratory thoracotomy for possible cancer) (Table 23-5).
Management of Anesthesia
Table 23-5 Comparison of Myasthenia Gravis and Myasthenic Syndrome | ||||||||||||||||||||||||||||
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V. Guillain-BarrÉ Syndrome (Polyaradiculoneuritis)
Guillain-Barré syndrome (polyradiculoneuritis) is the acute form of a group of disorders classified as inflammatory polyneuropathies (autoimmune disease caused by a bacterial or viral infection that triggers an immune response, producing antibodies that damage the myelin sheath and cause axonal degeneration).
This syndrome is characterized by the acute or subacute onset of skeletal muscle weakness or paralysis of the legs, which spreads cephalad and may result in difficulty swallowing and impaired ventilation from paralysis of the intercostal muscles.
The most serious immediate problem is hypoventilation. Vital capacity should be monitored frequently. If it
decreases below 15 to 20 mL/kg, mechanical ventilation of the lungs is indicated.
Although 85% of patients with this syndrome achieve a good recovery, chronic recurrent neuropathy develops in 3% to 5% of patients.
Autonomic nervous system dysfunction with wide fluctuations in blood pressure (physical stimulation may precipitate hypertension), tachycardia, cardiac dysrhythmias, and cardiac arrest.
Management of Anesthesia
Compensatory cardiovascular responses may be absent (autonomic nervous system dysfunction), resulting in significant hypotension secondary to postural changes, blood loss, or positive airway pressure. Conversely, stimuli such as laryngoscopy and tracheal intubation may produce hypertension and tachycardia.
SCh is not recommended because drug-induced potassium release may result in hyperkalemia and cardiac arrest. The response to nondepolarizing muscle relaxants ranges from sensitivity to resistance.
It is likely that mechanical ventilation will be required during the immediate postoperative period.
Table 23-6 The Most Frequently Encountered Types of Seizures | |
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Table 23-7 Anticonvulsant Drugs | |||||||||
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